The draft apparatus is indispensable for a spinning machine, and various trials have been made in connection with adapting the draft apparatus to be adapted to a ring spinning machine. A most important problem in the draft apparatus is how to reduce the draft unevenness having fatal influences on the yarn quality (uniformity, tenacity and the like).
According to the conventional drafting method, drafting is gradually accomplished through the roving step and the subsequent spinning step. However, because of the complicated process steps, this conventional method involves various disadvantages, for example, difficulty in maintenance and low productivity.
A five-line or six-line system omitting the roving step was once tried at a certain time after the Second World War. However, as is seen from the thesis entitled "Glories and Failures in Continuous Spinning" published in The Journal of the Japanese Association of Textile Machines (No. 2, 1979) five-line or six-line system draft apparatuses omitting the roving steps were proposed as new machines meeting the requirements in the art, but these attempts all met with failure. It is stated in the above thesis that even if an experimental operation is successful at such a high draft ratio as 400, in the actual operation the precise maintenance or control of the draft apparatus is very difficult, and various problems involved in the draft apparatus are pointed out in the thesis.
The spinning speed varies depending on whether the spinning machine is a ring spinning machine or a pneumatic spinning machine. It is said that in case of yarns of British count number of Ne 45, the highest spinning speed in the ring spinning method is 13 to 15 m/min and the highest spinning speed in the pneumatic spinning method is 180 to 200 m/min. The peripheral speed of the front roller of the draft apparatus is naturally determined according to this spinning speed, and the peripheral speed of the front roller is a value approximating to the spinning speed, though the value is changed to extent depending on such factors as the draft ratio. The following relation is established among the draft ratio D, the peripheral speed FV of the front roller and the peripheral speeds NV.sub.1, NV.sub.2, . . . NV.sub.n of other rollers: EQU D=FV/MV.sub.1.about.n
From the above formula, it will readily be understood that the peripheral speeds of the respective rollers satisfy the requirement of FV&gt;MV.sub.1.about.n and the peripheral speed of the front roller is much higher than the peripheral speeds of other rollers.
An air stream is produced in the vicinity of the nip point of each roller according to the peripheral speed of the roller. In the vicinity of the nip point of the front roller rotating at a much higher speed than the speeds of other rollers, a turbulent stream is produced, while laminar streams are produced in the vicinity of the nip points of other rollers.
The fiber arrangement of the sliver is disturbed by this turbulent stream and fibers are scattered, resulting in formation of fibers in which both the ends are not restricted but kept free or hooked fibers, and an undesirable phenomenon of abnormal expansion of the sliver width is often caused to occur.
The quantity of waste cotton is increased by such phenomenon and since hooked fibers are twisted in the hooked state, the tenacity of the resulting spun yarn is reduced and thick portions and thin portions are often formed in the spun yarn, resulting in reduction of uniformity. Moreover, the fibers which are twisted in the state where both the ends are not restricted but kept free make no contribution to the tenacity of the spun yarn, but they have bad influences on the yarn quality. For example, such fibers cause reduction of the uniformity and degrade the feel and touch of the spun yarn.